REM sleep in cubs - Lily's radio-collar

February 7, 2010 - 8:30 PM CST

The video** captured by Linda Gibson at 1 AM gave us the earliest opportunity we have ever had to watch a cub sleep.  A high percentage of the sleep was active (REM) sleep.  Every time we thought the cub was in quiet non-REM sleep, it would jerk, twitch, flex a paw, or vocalize.  Any dreams must have been pleasant because it even gave the contented motor-like hum at times.  Sleeping adult bears sometimes make this same sound.

We checked Google for REM sleep in infants and found , which may or may not be a scientific site.  It said infants have about 50% REM sleep compared with only 20% for adults and that REM sleep may promote brain development.  It said premature infants have an extra high proportion of REM sleep—about 90%.  We thought the cub was showing a proportion close to that.  Maybe that’s not surprising considering the premature state of newborn cubs and their need for rapid brain development to follow mom from the den about two months from now.

The good sighting of the cub on mom’s back is a harbinger of sightings to come as the cub gets more fur and the weather gets milder.  During the sighting the temperature was 12-14 F above zero.

During the day, with temperatures as high as 25, Lily was good enough to pull her head out from under her chest and reveal her face and radio-collar to any newcomers who had not seen that before.  Signals from the collar led us to her den and let us find her and walk with her when she is out of the den and active in summer.  Last fall, she was good enough to let us put this new collar on without tranquilizers, showing the same trust that allowed us to put the camera in the den without her getting defensive or abandoning the den.  We’ll see how long she keeps the collar on in the den.  Now, 4 months into hibernation, she has lost considerable weight, and the collar could slip off.  She is a remarkable bear that is giving all of us a better understanding of how bears live.

Thank you for your donations that will make more of this possible.

—Lynn Rogers and Sue Mansfield, Biologists, North American Bear Center